Handle connection for percussive tool



Sept. 2, 1958 J; J. CURRY ETAL HANDLE CONNECTION FOR PERCUSSIVE TOOL Filed Sept. 15, 1954 INVENTORS 1157 4 K0591! [III/90m ATTORNEYS United HANDLE (ZONNEC'HQN FTZR PERCUSSIVE TOOL Application September 13, 1954, Serial No. 455,528

3 Claims. (Cl. 305-32) The present invention relates in general to hand tools, and more particularly to an improved means for attaching the heads to the handles of percussive tools, such as hammers, hatchets, axes and the like, in such a manner that the union will be strong and invariable during the normal useful life of the tool. The present invention may also have application to tools which, although not primarily percussive, involve occasional large stresses in the region of the junction between the handle and metal components of the tool, such as shovels, hoes, rakes, and the like.

Traditionally, handles of percussive and like tools have been secured in position in the eye or handle recess of the tool head or working part by providing a diverging or outwardly tapering region adjacent the exit end of the eye and driving one or a plurality of wedges into the end of the handle so as to expand the same into the diverging eye portion and prevent withdrawal of the handle. Such traditional fastening means have long been known to be inadequate. Such a fastening expedient involves as an inherent incident thereto damage to the handle which adversely affects many of the physical properties which are desired to be retained. Further, the wedges that are driven into the end of the wooden handle to force it into contact with the metal working head tend to work loose, due most frequently to changes in humidity which cause alternate swelling and contraction of the wood with a gradual decrease in tightness. Additionally, these wedgefastening techniques present certain difliculties in maintaining uniform quality standards in mass production manufacture of such percussive tools. The wedges are generally driven into the handle ends by hand, and long experience in manufacturing such tools has indicated that the quality of the fastenings produced by such manual methods is noticeably impaired during the last several hours of each working day due to the tiring of the manual laborers.

The physical property of the Wooden handles in such tools which is most adversely affected by the wedge-securing technique is the horizontal or longitudinal shear resistance of the handle. It should be noted that in percussive tools, the handle is under a cantilever beam-type of loading in which, in the case of a hammer for example, the half of the eye section of the handle adjacent the poll and bell of the hammer is under tension during impact and the half disposed adjacent the claws is under compression. When wedges which are usually disposed along both the vertical and transverse axes of the handle have been driven into the eye section, the fibres are split along the longitudinal medial axis of the handle, generally at the neutral axis thereof, creating a fissure which severely reduces the horizontal or longitudinal shear strength of the handle. Without the Wedges, the interfibre bond so intercouples the tension and compression portions of the handle disposed oppositely from the neutral axis to provide relatively much greater longitudinal shear resistance.

-tates Patent Many expedients have been employed in an attempt to overcome these faults. They have included the prov1s1on of metal sleeves to hold the tool handle in place, the use of adjustable wedges which must be periodically driven by the owner of the tool to compensate for loosening of the joint, the use of metal handles, the casting of wedges in position in the tool, and the provision of rubber sleeves interposed between the handle and the head. None of these aforementioned expedients have proven to be entirely satisfactory.

The last-named expedient, that of providing cushioning material in the form of a sleeve entirely surrounding the portion of the handle projecting into the tool head eye, while originally considered to an etfective solution to this problem, has been found on careful examination to have some rather serious defects. Perhaps the most critical of these is that the resilient sleeve tends to isolate from the handle the vibrations set up in the tool head during impact. This isolation of the tool head vibrations in the case of hammers is so significant that the handle exerts no significant dampening effect on the tool head vibrations and the head tends to resonate, setting up a tuning fork effect in the claws which causes the claws to fracture. Additionally, since the tool head eye is spaced throughout from the handle surface, it would be extremely difiicult to maintain proper alignment between the handle and the tool head. Careful theoretical study of this assembly also reveals that it would be extremely difiicult to achieve satisfactory curing of the sleeve when poured in position between the tool head and the handle, since the annular regions between the handle and the eye adjacent both ends of the handle are open to permit free flow of the sleeve material from the eye, and there would not be sufficient back pressure to produce the desired pressure for proper curing.

The use of metal handles was found to be unsatisfactory because the center of gravity of the tool is shifted downwardly along the handle a much greater distance from the head than with wooden handles, and the highly beneficial elasticity and stress absorption characteristics of wood are lost.

Adjustable wedges are effective for only a short time after initial assembly of the tool because the hygroscopic wood tends to swell when picking up moisture as a result of high ambient humidity conditions. As the wood swells within the fixed volume of the tool head eye, the wood cells, which may be likened to minute ping pong balls, are collapsed as required to adjust for the increased volume of the handle due to the swelling of the wood. Subsequently, when the relative ambient humidity has reduced below that of the wood in the eye, the wood when giving up moisture will have a tendency to reduce in volume, with the result that a loosening of the assembly is elfected.

An object of the present invention, therefore, is the provision of a novel means for securing the heads to the handles of percussive tools which avoids the above-mentioned disadvantages.

Another object of the present invention is the provision of a novel means for securing handles to the heads of percussive tools which minimizes tendencies to loosen the handle in the eye due to external humidity variation.

Another object of the present invention is the provision of novel means for attaching handles to the heads of percussive tools, wherein physical damage to the wooden handle during assembly of the tool is minimized.

Another object of the present invention is the provision of novel means for securing handles to the heads of percussive tools involving the use of plastic resin adhesive compositions which are highly stable through the normally encountered variations in moisture or temperature, which effectively tolerate the shear and impact stresses to 3 which the tool is subjected and which effectively transmit the vibrations from the tool head to the handle to attenuate resonant vibrations in the head.

Another object of thepresent invention is theprovision ofznovefl meansfor securing handles .to toolheads .of percussive tools involving the zuseofadhesive compositionssuitable to be poured. or injected. into. cavitiesz formed therefor by the handle and toolhead -eye, thereby-alleviating the necessity of manually forcing wedges or the like. into the-handle.

Other objects, advantages and capabilities ofthe present invention will .become apparentfrom ,the following detailed description, taken in conjunctionwith the .accompanying drawing, illustrating'one preferred embodimentof. the invention.

.In the drawing:

Figure .1 is a perspectiveviewof.ahammer, whereinthe hammer head-and handle are-united in accordance with the present invention.

Figure 2 is a fragmentary longitudinal section view taken along the lines 22 ofFigure 1; and

Figure 3 is a fragmentary transverse section view taken along the lines 33 of Figure 2.

Referring to the drawing, whereinlike referencecharacters designate corresponding parts'throughoutthe several figures, thereis illustrated a clawihammengenerally indicated by the referencecharacter 10,which.is especially constructed to facilitate the incorporation of certain plastic :resin adhesive compositions, .to be ;hereinafter described, as the bonding medium between thehead ,11 andhandle 12.0f .the'claw hammer. The hammerhead 11 employed in .the present invention is provided with the usual poll and bell 13, bifurcated claws '14, and central portion 15 having a downwardly projecting boss 16. Extending along'an axis perpendicular to the medial axis of the poll and bell 13 and through the central portion 15 and boss 16 is the usual eye .17, the Wallsof which diverge slightly to the exit end -19 of the. eye from a breaking point '18 lying approximately-K; to /2 inch from .the exit end 19, producing a. diverging surface region 20 which sweeps back approximately /32 .Of an inchalong its-total extent relative to the projected plane of the remaining surface region 21 of the eye extending from the breaking point 18 to the entrance :end22 of the :eye. This is the conventional hammer head .construction normally used in connection with the Wedgetype -.of securing technique'for hammers and other percussive tools.

The portion 23 of 'the handle 12 which ;is designed to be fittedinto the-eye 17 of the head His modifiediin design to adapt the hammer to receive a} plastic resin adhesive compound for bonding the handleto thehammer head. To this end, the lateral faces 24 of thesubstantially rectangular cross section portion 23 of'thefhandle designed to be projected into the .eye 17 are shaped 'in the .usual way so that handle surface :portions .;in the region 25 extending from the outer end thereof :to approximately /4 inch from the entrance end 22 .oftheeye are spaced slightly from the. coextensive adjacentgsurfaces of the eye 17; The remaining surfaceqportions in .the region 26 of the eye section 23 'of1the handle .idiverge slightly from the point approximately A ;inchiinsideithe eye .to a greater cross section than that of-the ientrance end 22 of the eye and is in intimate frictional engagement throughout with the eye surface region 21. when the handle eye section 23 is forcibly driven to .its full.

extent, within the eye. Inaceordance with conventional practice, the handle 12.is driven into .the eye 17 :of the head 11. to a point where the entrance -end 22of theeye 17 .begins to peel back the wood, thelburrs 27 formed at the entrance 22 thereby forming aseal which extends en tirely around the junction between-the entrance of'the eye 17 and the handle '12.

.As is illustratedinFigure 2, the eye-seetion2-3. of thehandle iscut .to a length and in a. plane paralleltoit'he 4 7 plane through the front and rear edges of. the exit end of the eye that when the sealing burr 27 and shoulder formed at the entrance 22 of the eye is sufficient to sub- V the complementarysurface regions of theeye 17, amp

or cavity which opens through the exit-end 19 of theeye and is sealed at and immediately inside of=.the entrance I end .22 .of the .eye. .Into this cavity .is introduced a plastic'resin adhesive composition, indicated at'29; which, when cured, forms avsubstantiallypermanent bond between the eye portion 23 of the handle. and the eye 17 of the hammer head 11 which resists any loosening of the handle in .the hammer head and retards adverse :action of humidity variationon the eye portion ofthechan'dle.

Thebasic resin component of the plastic resin adhesive composition employedinaccordance with the presentinvention for .bondingtthe handle 12 and head 11 of 'the hammer is.drawn from'the epoxy resin family. Epoxy resins arebased on ethylene-oxide or its .homologsmr derivatives and are .characterized by a-.chain:molecule which .has an epoxy group ,at each 'end. ..Typical .of these, .andthe epoxy resin which is :employe'd'in the-.pneferred embodiment of the present invention, is the com pound made by condensation of .epichlorohydrin .'(1-

chloro -.2,3*-. epoxypropane) and bisphenol .A 2,2-p=hydroxyphenylpropane) reacted at about '100".C..in the presence of sodium hydroxide. The epichlorohydrin-1h a coproduct .obtainedduring the process of producing glycerolfrom petroleum. In producing thexepoxyzresin, the epichlorohydrin is reacted with bisphenol in;an averageproportion of .0.8 .lb. of bisphenol to .0.4.lb. epichlorohydrin to obtain one pound of epoxy resin. Thiscompound, which will be hereinafter termed iepichlorohydrinbisphenol, is acommercially availablecorm pound, and is prepared intoa production-mixture for;use in .one preferred embodiment of the-present: inventioniby mixing v9.1 grams ,of black .dye 'with 40 pounds .of vthe epichlorohydrin bisphenol. It is understood, .however, that othertintingadditives may beused, .or that the-commercially .obtainable epichlorohydrin bisphenolzunmixe'd with .other .compounds may be used, without .in ianyiway altering. the efiectiveness'of. the adhesive.

.A.special promoter and-modifier mixture to be :added to .themixture of epichlorohydrin bisphenol :and .black dye .in the preferred embodiment is formed .ofanzamine promoter such as triethylene tetramine and a synthetic rubber modifier such asThiokol liquid polymer, a condensation polymer of ethylene dichloride and'a polysulfide such as sodium tetrasulfide, whose average structure'may be represented by:

HS-'( C H -O-CH O-C H -S-S) -C H -O-CH -O-C H SH An example of this promoter andmodifier mixture is formed .of 34.5 pounds of Thiokol and 5.5 pounds of triethylenetetramine mixed together to produce 4(Lpound lots of the mixture.

The. final adhesive mixture to'be applied to'the hammer head-and handle is blended immediately prior to addition to the hammer by mixing, as .aniexample, 16.8 grams or 42% of the promoter and modifier mixture formed of Thiokol and triethylene tetramine and 23.2 grams or 58% of the above-mentioned ,production mixture 7 consisting .of epichlorohydrin .bisphenol and black dye.

Broken down into its various.components,-a 40-gran1 sample adhesive compound to be employed in thepreferred embodiment of the present invention consists of 14.5 grams of the Thiokol modifier, 2.3 grams of the triethylene tetramine promoter, and 23.2 .gramsof the epoxy production mixture formed of 40 pounds .of epichlorohydrin bisphenol and 91 grams of black dye.

In the practice of one preferred embodiment of the invention, the claw hammer heads 11 are preheated to approximately 200 F. in any conventional manner, as by placing them on an electric hot plate. The purpose of preheating the tool head is to increase the curing or hardening rate of the epoxy plastic resin, with the result that delays in production from excessive curing time are reduced. The hammer heads may be preheated either with the handles already driven into the eyes of the tool head or with the tool heads separate from the handles.

The hammer heads 11 with the handles 12 driven therein are then hung on racks in a vertical position to permit the epoxy adhesive composition, prepared in the manner described above, to be poured or injected into the upwardly opening cavity formed adjacent the upwardly facing exit end 19 of the tool head 17 and the bounding region between the facing portions of the handle and tool head eye in the surface regions 25 and 20. The resin may be easily dispensed into this cavity by placing the resin in a plastic bottle onto which a ribbon top cap and spout are afiixed so that the proper amount of plastic resin can be accurately admitted to the cavity in the tool head eye. Since polymerization of the adhesive compound begins to take place immediately when the promoter and resin are added together, and the average period before the compound begins to set to an undesirable degree is one-half hour, the production mixture of the epoxy resin and dye should not be mixed with the promoter mixture until immediately before filling of the cavity in the hammer head eye.

The poured tools are then allowed to remain on the racks for a period of time ranging from 4 hours to overnight, depending upon the temperature to which the tool heads have been preheated. It is to be understood that the preheating operation may be entirely eliminated if it is convenient to permit the tools to remain at rest for a curing period of the order of eighteen hours. Following the curing period, the tools are chipped, wiped, inspected, and are ready for shipment to customers. By the use of the epoxy technique of assembly, the employment of manual labor required for the many operations involved in conventional handle assembly techniques is eliminated completely.

Other amine accelerator catalysts which can be used with the Thiokol liquid polymer to form a modifier and promoter component to be added to the epoxy resin, instead of the triethylene tetramine mentioned above are: tri-dimethylaminomethylphenol or less active amines such as, in decreasing order of reactivity, diethylenetriamine, dimethylaminopropylamine, dimethylaminomethyl-phenol, benzyldimethylarnine, piperidine, diethylamine, dimethylaminopropionitrile, and pyridine.

The incorporation of the T hiokol liquid polymer modifier, which is a synthetic rubber, to the epoxy formulation is for the purpose of increasing the cold temperature shock resistance of the compound to a satisfactory range. Without the Thiokol modifier, the checking resulting from cold temperature shocking when the cured assemblies were thermally shocked by exposing them alternately to heat and cold in the order of F. to 80 F., while it had no adverse effect on the shear strength, did result in a considerable reduction in the resistance to impact. The formulation employing the Thiokol liquid polymer was found to be completely successful in overcoming these cold temperature deficiencies.

Exhaustive tests have indicated that in addition to having good resistance to cold temperature cracking resulting from differences in the linear coeflicient of expansion between the wood, the cured epoxy resin, and the metal tool head, the hammer constructed in accordance with the present invention was found to have very good characteristics when subjected to cantilever loading, shear, impact, solubility, and moisture and high temperature dimensional stability tests. The epoxy resin composition 29, when cured in the form of the downwardly facing cup defined by the associated surfaces of the handle eye portion 23 and eye 17, produces a strong intimate bond between the head 11 and handle 12, which possesses sufficient resilience to resist cracking under thermal shock. By this construction, vibrations are transmitted from the head to the handle to give the tool a proper feeland to prevent confining the vibrations to the hammer head where they will resonate and produce a tuning fork efiect in the claws, causing untimely fracture of the claws. The addition of the black dye to the epoxy resin in the manner described above tints the resin to match the color of the tool head, thereby producing a neat and attractive tool, in addition to the advantages enumerated above.

It has been found to be advantageous in certain situations to add a solvent such as toluene and toluol in a pecentage of about 2 to 5% by weight of the epichlorohydrin bisphenol resin only prior to pouring or injecting the epoxy formulation into the hammer eye cavity. Such solvents reduce the viscosity of the epoxy formulation and therefore aid in wetting out the adjacent surfaces of the tool head and handle eye sections, thereby facilitating the pouring or injection of the epoxy mixture into the eye cavity.

While but one particular embodiment of the invention has been particularly shown and described, it is apparent that various modifications may be made in the invention without departing from the spirit and scope thereof, and it is desired, therefore, that only such limitations shall be placed thereon as are imposed by the prior art and are set forth in the appended claims.

We claim:

1. A percussive tool comprising a metallic head with a handle-receiving eye therethrough having entrance and exit ends, a handle having an end portion within the eye in pressure tight contact with the head over an area adjacent the entrance end of the eye and spaced from the head adjacent the exit end of the eye to provide a closedbottom cavity open to the exit end of the eye and encircling the handle end portion, and a body of bonding material including epoxy resin filling the cavity whereby the head is bonded to the handle and the handle has intimate contact with the metallic head to dampen vibrations set up in the head by impact shock.

2. A percussive tool comprising a metallic head with a handle-receiving eye therethrough having entrance and exit ends, a handle having an end portion within the eye in pressure tight contact with the head over an area adjacent the entrance end of the eye and spaced from the head progressively increasing distances from the area of contact toward the exit end of the eye to provide a closedbottom cavity having outwardly diverging walls and open to the exit end of the eye and encircling the handle end portion, and a body of bonding material including epoxy resin filling the cavity, whereby the head is bonded to the handle and the handle has intimate contact with the metallic head to dampen vibrations set up in the head by impact shock.

3. A percussive tool comprising a metallic head with a handle-receiving eye therethrough having entrance and exit ends, a handle having an end portion within the eye but terminating short of the face of the head at the exit end of the eye, the end portion being in pressure tight contact with the head over an area adjacent the entrance end of the eye and spaced from the head progressively increasing distances from the area of contact toward the exit end of the eye to provide a closed-bottom cavity having outwardly diverging walls and open to the exit end of the eye and encircling the end portion, and a body of bonding material including epoxy resin filling the handle-encircling cavity and the eye substantially flush with the face of the head at the exit end of the eye to form a cap of bonding material enclosing the outer end of the handle end portion and having a skirt of tapering 

